Lower limb is the lower part of human body, comprising hip, thigh, knee joint, shank and foot. The lower limb performs a function of supporting the human body while standing or walking and enables the human body to be in many kinds of postures such as sitting, kneel sitting and prone. The main parts of the human body for supporting the weight of the body are bones of lower limbs, namely lower limb bones, which include the bone of lower limb girdle and the bones of free lower limbs. The bone of lower limb girdle is the innominate bone, and the bones of free lower limbs include femur, patella, tibia, fibula, seven tarsal bones, five metatarsal bones and fourteen toe bones. A connection part of bones is called a joint, and there are three main joints in the lower limb: hip joint, knee joint and ankle joint. All of the three joints are weight-bearing joints.
The bones or joints of lower limb in a human body may suffer lesion or degeneration because of aging, diseases and accidents. The lesion or degeneration of lower limb joints may affect their weight-bearing function, and may further affect standing, walking, running and jumping of human body. In this situation, drug therapy, traditional physical therapy and rehabilitation therapy are always applied, and in serious situation operative treatment is applied to recover the function of lower limb bones or joints as well. In a rehabilitation therapy, an orthosis is always used.
Orthosis, also known as brace, is an in-vitro device used at human limbs or other locations to prevent and correct deformity, cure diseases of bones, joints and nervus, and compensate their functions. The orthosis can relieve the dysfunction of limbs, spine and musculoskeletal system by restricting or assisting body movement or by changing the force line of human body. According to different application locations, the orthosis can be divided into three classes: upper limb orthosis, spinal orthosis and lower limb orthosis. In the three kinds of orthosis, the upper limb orthosis is mainly used to compensate the loss of muscle strength, support the paralytic body, keep and hold limbs or postures, supply traction to prevent contracture and prevent or correct deformity; the spinal orthosis is mainly used to relieve regional pain, protect diseased region from further injury, support the paralytic body and prevent or correct deformity; the lower limb orthosis is used to fix the diseased joints, prevent or correct deformity, compensate for the loss of muscle strength, improve the gait, prevent limbs from bearing weight, promote fracture healing and function recovery.
The knee joint is one of the significant weight-bearing joints in lower limbs. As shown in FIG. 1, the knee joint connects femur 1 in the thigh and tibia 2 in the shank, comprising an articular cartilage 4, a medial meniscus 5 and a lateral meniscus 6. According to kinesiology analysis, there are many kinds of movement in the knee joint when the lower limb changes from a bend status to a straight status. For example, when the shank wiggles, the bend angle of passive bend is 0˜140°; meanwhile the thigh can rotate an angle around the long axis of the shank, which is called internal rotation and external rotation, and the angle is about 30° in the situation of initiative rotation.
The inner structure of knee joint may be damaged by the reason of external force impact or degeneration and diseases such as ligamentous injury, cartilaginous degeneration and meniscus wear, and knee pain and dyskinesia may further occur. To solve the above-mentioned problems, knee joint assistive devices are designed for different diseases or injuries. For example, PCL and ACL assistive devices designed for cruciate ligament injury, and nonbearing assistive devices (orthosis) designed for knee osteoarthritis. So far, most of knee joint assistive devices (orthosis) comprise two lateral hinges, whose rotation planes are parallel, to connect thigh frame and shank frame without considering the internal rotation and external rotation between the thigh and the shank, so such assistive devices can only perform a rotation along the rotation planes of lateral hinges. When patients wear such assistive devices, their movement of the internal rotation and external rotation between thigh and shank will be restricted, and the force balance in the knee joint will be changed. Odra from France has designed an assistive device which can perform a proactive internal rotation (seen on the website www.odra.ca/en/) shown in FIG. 2. However, the angle of internal rotation is constant, which is not fit for everybody, and the space between the lateral hinge and the knee joint is so large that low fitness and poor appearance are caused, which affects the acceptability of users.
Moreover, most assistive devices need to put a force from the front direction on the shank so as to fix the shank, so these devices comprise a shank bracket with soft belts or curved rigid structure to press the shank. Since the tibia will bear a large pressure, and the soft tissue layer of the front position of the shank is too thin that the position is sensitive to pressure, the existing assistive devices are poor in comfort.
Therefore, technical personnel are working at developing a knee joint protecting device, which can fit for the movement of knee joint and increase the comfort of shank in wearing.